1. Field of the Invention
The invention relates to a combustion control system typically used with a combustion apparatus such as a boiler, a heater or the like.
2. Description of the Prior Art
It is known to mechanically connect the valves of a boiler controlling fuel feed and air intake in order to establish a definite and selectable air to fuel or oxygen to fuel ratio. The simplest and least expensive combustion control system is known as the "jackshaft" positioning system. This system consists of a mechanical linkage arrangement in which a master arm is connected to a main shaft for controlling the fuel valves and a slave arm is connected to the air damper and is responsive to the main shaft through an intermediate linkage strut. Such a mechanical arrangement establishes a master-slave relationship between the fuel valves and air damper. The intermediate linkage strut of the prior art system is adjusted, to provide a fuel to air ratio which remains generally satisfactory through all load requirements of the combustion apparatus.
However, in order to maximize combustion process efficiency through various load requirements, changes in the BTU value of the fuel, viscosity of the fuel, combustion air temperature, burner clogging, etc., the original calibrated relationship between fuel and air must be adjusted. Such an adjustment is often referred to as an oxygen trim adjustment and may be necessary several times a day. While such adjustments can be effected by changing the interconnecting points at the opposite ends of the linkage strut, such mechanical manipulation is obviously time consuming and necessitates a recalibration of the jackshaft positioning system.
It is also known to utilize a jackshaft positioning system which includes a cam mechanism inserted between the jackshaft and the air or fuel valves. In such an arrangement, a limited degree of predetermined variance can be established in the air to fuel relationship through the geometry of the cam mechanism. While some degree of modification to the air-fuel ratio is available, the aforedescribed problems relating to changes in the BTU value of the fuel, viscosity of the fuel, combustion air temperature, etc., still demand that original calibrated relationship between fuel and air be adjusted. The frequent mechanical modifications to the cam mechanism necessary to provide the adjustments to the original calibrated relationship is not a useful solution for these problems.
It is taught in U.S. Pat. No. 4,249,886, which patent is assigned to the assignee of the present application, that an angularly modifiable trim link can be incorporated into a jackshaft positioning system. The trim link allows the conventional master-slave relationship between the fuel control and damper control means to continue. In addition to the conventional fixed master-slave relationship, the trim link effects slight adjustments to the damper means in order to better regulate the air-fuel ratio. The specific articulation of the trim link is controlled by a trim positioner means which is responsive to a control system.
U.S. Pat. application Ser. No. 392,978, now U.S. Pat. No. 4,479,774, assigned to the assignee of the present invention discloses a combustion control system which includes a linkage strut adjustor apparatus that modifies the air-fuel ratio. This adjustor apparatus is remotely actuated and includes an overload protection cylinder which minimizes the possibility of mechanical damage to either the adjustor apparatus itself or the jackshaft system.
It is an object of this invention to provide an improved jackshaft controlled boiler control system which maintains an optimum air-fuel ratio relationship at all boiler loads.
It is also an object of this invention to utilize a programmable control system responsive to external computation, such as boiler load index, and flue gas analysis to establish an optimum air-fuel relationship at all boiler loads.
It is still a further object of this invention to disclose a method of programming a programmable control system in order to establish and maintain automatically thereafter the efficient and effective control of a jackshaft controlled boiler control system.